1. Field of the Disclosure
The disclosure relates to devices for immobilizing two or more vertebrae relative to one another to promote fusion of the vertebrae. The devices and improvements described herein may also be used with other types of bone plates or instrumentation.
2. Related Art
Adjacent vertebrae may be surgically joined together in a fusion procedure. The procedure may join two (bi-level) or more (multi-level) vertebrae. During the surgery, the vertebrae are fixed in position relative to one another with a plate or other instrumentation, and a bone graft is placed between the vertebrae. The bone graft will promote new bone growth between the vertebrae, and eventually the bones will grow together, which typically takes 6-18 months after the surgery.
More commonly, fusion of vertebrae is used as part of a treatment for a herniated disc, rheumatoid arthritis, infection, tumor, or other condition resulting in spinal deformities. In each case, the primary disease is treated before the fusion procedure. In the case of a herniated disc or degenerative disc disorder, for example, the intervertebral disc is removed (a procedure known as a discectomy). After the discectomy, the instrumentation is attached to the vertebrae. The two related procedures are typically performed as part of the same surgery, to minimize trauma and expense to the patient.
Many devices are available for instrumentation of the spine in a fusion procedure. Current spinal plates, however, suffer from one or more limitations. For example, there are often situations and size restrictions that limit the number of screws that can be used in a design or surgery. Fewer screws results in lower stability of the plate.
One solution to this problem has been to add spikes or other sharp features to the plate. The spikes increase the stability of the bone-plate interface, as well as the stability of the underlying bone structures. There is a risk, however, that the sharp features may puncture or damage blood vessels, nerves, or other delicate anatomical structures during placement. There is also a difficulty for the surgeon to determine how well the plate will rest on the bone surface without first inserting the spikes into the bone.
Spinal plates are commonly fixed to bone with bone screws. Many modern plate designs incorporate blocking set screws, which prevent the bone screws from backing out of the bone after they have been implanted. Blocking set screws, however, do not prevent the bone screws from rotating. It is possible for the bone screws to rotate and loosen while they are held in place by the set screws. Loose bone screws reduce the stability of the bone-plate interface, thereby reducing the chance of a successful fusion procedure.
Accordingly, there is a need for a bone plate that provides enhanced stability and prevents rotation of the bone screws holding the plate to the bone.